Evidence from unexpected temporary school closures and reduced instruction time suggests school closures will reduce educational achievement, both in the short and long term. Children from disadvantaged backgrounds are likely to be affected more than others by school closures, with fewer family resources and less access to online learning resources to offset lost instruction time. In England, the total cost of the resources lost in each week of state school closure is more than £1 billion. Educational deficits from time lost to school shutdowns can be made up with additional hours of teaching when schools reopen, though schools might need to put back more hours than were lost and it may not be feasible to do this within the traditional school year. Compensating lost instruction time through additional resources, without additional hours, is likely to be even more expensive.